Read out integrated circuit

ABSTRACT

According to one embodiment, a circuit comprises a Capacitive Trans-Impedance Amplifier (CTIA) configured to receive a current pulse at an input and convert the current pulse to a voltage step. The voltage step is directed to a first signal path and a second signal path. When the voltage step exceeds a first threshold, the first signal path directs an enable pulse to the second signal path. The second signal path generates an output pulse when the voltage step exceeds a second threshold and the enable pulse is enabled. The second signal path comprises a first, a second, and a third amplifier to increase detection of the voltage step by the second signal path.

GOVERNMENT FUNDING

The U.S. Government may have certain rights in this invention asprovided for by the terms of Contract No. FA8632-05-C-2454 awarded bythe (AFRL) Air Force Research Lab, (MDA) Missile Defense Agency atKirkland AFB in Albuquerque, N. Mex.

TECHNICAL FIELD

This invention relates generally to the field of integrated circuits andmore specifically to a read out integrated circuit.

BACKGROUND

A Read Out Integrated Circuit (ROIC) may receive sensor data from asensor, transform the sensor data, and transmit the transformed data toexternal electronics. As an example, the ROIC may be configured in aLaser Detection and Ranging (LADAR) system operable to track a targetobject using laser signals. The ROIC may receive an analog current pulsedescribing a location of the target object, transform the analog currentpulse to a digital voltage pulse, and transmit the digital voltage pulseto a display.

SUMMARY OF THE DISCLOSURE

According to one embodiment, a circuit comprises a CapacitiveTrans-Impedance Amplifier (CTIA) configured to receive a current pulseat an input and convert the current pulse to a voltage step. The voltagestep is directed to a first signal path and a second signal path. Whenthe voltage step exceeds a first threshold, the first signal pathdirects an enable pulse to the second signal path. The second signalpath generates an output pulse when the voltage step exceeds a secondthreshold and the enable pulse is enabled. The second signal pathcomprises a first, a second, and a third amplifier to increase detectionof the voltage step by the second signal path.

According to one embodiment, a circuit comprises a ResistiveTrans-Impedance Amplifier (RTIA) configured to receive a current pulseat an input and convert the current pulse to a voltage pulse. Thevoltage pulse is directed to a first signal path and a second signalpath. When the voltage pulse exceeds a first threshold, the first signalpath directs an enable pulse to the second signal path. The secondsignal path generates an output pulse when the voltage pulse exceeds asecond threshold and the enable pulse is enabled. The second signal pathcomprises a first and a second high pass amplifier to increase detectionof the voltage pulse by the second signal path.

Some embodiments of the disclosure may provide one or more technicaladvantages. In some embodiments, an output signal may be generated whenan input signal and an enable signal are detected at substantially thesame time. In some embodiments, amplifiers may sharpen a waveform of theinput signal, which may improve synchronization with the enable pulse.In this manner, the output signal may be generated more accurately.

Some embodiments may benefit from some, none, or all of theseadvantages. Other technical advantages may be readily ascertained by oneof ordinary skill in the art.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention and itsfeatures and advantages, reference is now made to the followingdescription, taken in conjunction with the accompanying drawings, inwhich:

FIG. 1 illustrates an example of a Laser Detection and Ranging (LADAR)system comprising a high-pass amplifier;

FIG. 2 illustrates an example of a circuit comprising a CapacitiveTrans-Impedance Amplifier (CTIA) and a high-pass amplifier;

FIG. 3 illustrates examples of signals generated by the circuit of FIG.2;

FIG. 4 illustrates an example of a method for generating an output pulseusing a circuit comprising a CTIA and a high-pass amplifier;

FIG. 5 illustrates an example of a circuit comprising a ResistiveTrans-Impedance Amplifier (RTIA) and a high-pass amplifier;

FIG. 6 illustrates examples of signals generated by the circuit of FIG.5; and

FIG. 7 illustrates an example of a method for generating an output pulseusing a circuit comprising an RTIA and a high-pass amplifier.

DETAILED DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention and its advantages are bestunderstood by referring to FIGS. 1-7 of the drawings, like numeralsbeing used for like and corresponding parts of the various drawings.

FIG. 1 illustrates an example of a Laser Detection and Ranging (LADAR)system 10. In some embodiments, system 10 may comprise a LADAR 20configured to detect a target object 40. For example, the LADAR 20 maytransmit a laser signal 24 that may impinge on a surface of the targetobject 40 and may be reflected back toward the LADAR 20 as a returnsignal 26. In some embodiments, the LADAR 20 may determine athree-dimensional location of the target object 40 according to theangle at which the return signal 26 is received and/or the amount ofdelay in receiving the return signal 26.

In some embodiments, the LADAR 20 may comprise a signal generator 22, asensor 28, and a Read Out Integrated Circuit (ROIC) 30. The signalgenerator 22 may generate any suitable laser signal 24, such as aninfrared laser pulse. The laser signal 24 may be transmitted accordingto a scan pattern that traverses a two-dimensional area. In someembodiments, the laser signal 24 may impinge on a surface of the targetobject 40 and may be reflected back toward the LADAR 20.

The sensor 28 of LADAR 20 may detect the return signal 26. In someembodiments, sensor 28 may comprise a focal-plane array of light-sensingpixels. The focal-plane array may detect photons of a particularwavelengths, such as infrared wavelengths, and may generate an analogcurrent pulse according to the number of photons detected at each pixel.

In some embodiments, the analog current pulse may be transmitted fromthe sensor 28 to the ROIC 30. The ROIC 30 may comprise an amplifiersystem 32 for transforming the analog current pulse to a digital voltagepulse. The digital voltage pulse may be transmitted from the ROIC 30 toother equipment, such as a display 50 configured to provide a user withinformation describing a three-dimensional location of the target object40.

Modifications, additions, or omissions may be made to the systemdescribed without departing from the scope of the invention. The systemmay include more fewer, or other components. Additionally, componentsmay be integrated or separated. For example, in some embodiments thesignal generator 22 may be external to the LADAR 20. As another example,in some embodiment the display 50 may be located within the LADAR 20.

FIG. 2 illustrates an example of a circuit 100 comprising a CapacitiveTrans-Impedance Amplifier (CTIA) pulse integrator 108 and a high-passamplifier. In some embodiments, the circuit 100 may be used as theamplifier system 32 of FIG. 1.

In some embodiments, circuit 100 may receive an analog current pulse104, such as a current pulse 104 generated by a sensor of a LADAR. Thecurrent pulse 104 may be received by the CTIA pulse integrator 108,where it may be converted to a voltage step 112. The voltage step 112may be directed to a first signal path 116 and a second signal path 140.

In some embodiments, the first signal path 116 may generate an enablepulse 136 configured to enable the second signal path 140 to generate anoutput pulse 172. The first signal path 116 may comprise a low-noise,high-pass amplifier 120 and a first path comparator 128. In someembodiments, the amplifier 120 may filter the voltage step 112 to yielda filtered voltage pulse 124. For example, the amplifier 120 may allow asignal comprising higher frequencies to pass and may filter out noisecomprising lower frequencies.

In some embodiments, the filtered voltage pulse 124 may be directed tothe first path comparator 128. The first path comparator 124 may enablethe enable pulse 136 when the filtered voltage pulse 124 exceeds a firstthreshold 132. The first signal path 116 may be configured to minimizedetection of a false pulse. As an example, the first threshold 132 maybe relatively high, such as a threshold in the range of 50 mV to 500 mV(referred to the output 124 of the high-pass amplifier 120). As anotherexample, the bandwidth of the amplifier 120 may be relatively small tofilter out the relatively low frequencies.

The bandwidth of the amplifier 120 may be characterized by a roll-onfrequency and a roll-off frequency. The roll-on frequency may be afrequency below which the signal is attenuated. In some embodiments, theattenuation may be incremental such that frequencies slightly lower thanthe roll-on frequency are less. attenuated than frequenciessignificantly lower than the roll-on frequency. The roll-off frequencymay be an upper cut-off frequency of the amplifier 120. Thus, theroll-off frequency may be greater than the roll-on frequency. In someembodiments, the amplifier 120 may have a roll-on frequency in the rangeof 10 to 100 MHz and a roll-off frequency in the range of 20 to 500 MHz.

In some embodiments, the second signal path 140 may comprise a secondpath comparator 168 configured to generate a digital output pulse 172when the enable pulse 136 of the first signal path 116 is enabled andthe voltage step 112 received from the CTIA pulse integrator 108 exceedsa second threshold, such as a threshold in the range of 5 mV to 50 mV(referred to the CTIA output). In some embodiments, the voltage step 112may be passed through a series of high-pass amplifiers to yield a higherresolution voltage pulse 164 to be used as an input of the second pathcomparator 168.

The series of high-pass amplifiers may comprise any suitable number ofamplifiers to yield a desired waveform. In some embodiments, the seriesof high-pass amplifiers may comprise a first amplifier 144 configured togenerate a first waveform 148, a second amplifier 152 configured togenerate a second waveform 156, and a third amplifier 160 configured togenerate the higher resolution voltage pulse 164. In some embodiments,the amplifiers may have a larger bandwidth than the low-noise, high-passamplifier 120 of the first signal path 116. In some embodiments, theamplifiers may have a roll-on frequency in the range of 50 to 500 MHzand a roll-off frequency in the range of 100 to 5000 MHz.

The relatively large bandwidth of the amplifiers of the second signalpath 140 may allow more frequencies to pass thereby yielding a higherresolution signal. The larger bandwidth, however, may allow increasednoise to pass and may potentially cause a false pulse to be detected. Toprevent the false pulse from being transmitted as the output pulse 172,the second path comparator may generate the output pulse 172 only whenthe enable pulse 136 is enabled. That is, the first signal path 116 maybe configured to detect a valid pulse and to apply time domain filteringto gate the second signal path 140 when the valid pulse is detected.

In some embodiments, the first signal path 116 may experience moresignaling delay than the second signal path 140. For example, thesmaller bandwidth of amplifier 120 may introduce more signaling delaythan the amplifiers 144, 152, and 160. Accordingly, the amplifiers 144,152, and 160 of the second signal path 140 may be selected to improvesynchronization with the first signal path 116. For example, the thirdamplifier 160 may be configured to narrow a pulse width and to increasean amplitude of the voltage pulse so detection of a voltage peak occurswhen a corresponding enable pulse 136 is enabled.

FIG. 3 illustrates an example of signals generated by the circuit ofFIG. 2. In some embodiments, the voltage step 112 may be output from theCTIA pulse integrator 108 and may be directed to the first signal path116 and the second signal path 140. The first signal path 116 may directthe voltage step 112 to the low-noise, high-pass amplifier 120 to yieldfiltered voltage step 124. The first path comparator 128 may enable theenable pulse 136 when the filtered voltage pulse 124 exceeds the firstthreshold 132.

The second signal path 140 may direct the voltage step 112 to the firstamplifier 144 to yield the first waveform 148. The first waveform may bedirected to the second amplifier 152 to yield the second waveform 156.The second waveform may be directed to the third amplifier 160 to yieldthe higher resolution voltage pulse 164. In some embodiments, the higherresolution voltage pulse 164 may have a narrower pulse width and alarger voltage peak than the first waveform 148 and the second waveform156. In some embodiments, the higher resolution voltage pulse 164 mayhave an inverted peak.

FIG. 4 illustrates an example of a method 200 for generating an outputpulse using a circuit comprising a CTIA pulse integrator and a high-passamplifier. The method may begin at step 204 where a CTIA pulseintegrator receives a current pulse. At step 208, the CTIA pulseintegrator may convert the current pulse to a voltage step byintegrating a charge of the current pulse.

The voltage step generated by the CTIA pulse integrator may be directedto a first signal path and a second signal path at step 212. The firstsignal path may generate an enable pulse at step 216 when the voltagestep exceeds a first threshold. In some embodiments, the first signalpath may be configured to minimize the likelihood of the detecting afalse pulse. For example, the first threshold may be relatively high toprevent the first signal path from enabling the enable pulse due to thedetection of noise, rather than the signal. At step 220, the enablepulse may be directed to the second signal path.

The second signal path may receive the voltage step from the CTIA pulseintegrator and may filter the voltage step at step 224. In someembodiments, the second signal path may filter the voltage step with afirst, a second, and a third high-pass amplifier to yield a higherresolution voltage pulse. For example, the first, second, and thirdamplifiers may have a relatively large bandwidth to allow lowerfrequencies, which may potentially be signal or noise, to pass. In someembodiments, passing the signal through the series of amplifiers maysharpen the waveform by narrowing the pulse width and/or increasing thepeak amplitude. The sharpened waveform may allow for better detection ofthe voltage peak.

At step 228, the second signal path may generate a digital output pulsewhen the higher resolution voltage pulse exceeds a second threshold andthe enable pulse is enabled. In some embodiments, the sharpened waveformreceived from the third amplifier of the second signal path may allowthe peak of the higher resolution voltage pulse to be detected atsubstantially the same time that a corresponding enable pulse isenabled. Upon generation of the output voltage, the method ends.

Modifications, additions, or omissions may be made to the methodsdescribed without departing from the scope of the invention. The methodsmay include more, fewer, or other steps. Additionally, steps may beperformed in any suitable order.

FIG. 5 illustrates an example of a circuit 300 comprising a ResistiveTrans-Impedance Amplifier (RTIA) 308 and a high-pass amplifier. In someembodiments, the circuit 300 may be used as the amplifier system 32 ofFIG. 1.

In some embodiments, circuit 300 may receive an analog current pulse304, such as a current pulse 304 generated by a sensor of a LADAR. Thecurrent pulse 304 may be received by the RTIA 308, where it may beconverted to a voltage pulse 312. The voltage pulse 312 may be directedto a first signal path 316 and a second signal path 328.

In some embodiments, the first signal path 316 may generate an enablepulse 324 configured to enable the second signal path 328 to generate anoutput pulse 352. The first signal path 316 may comprise a first pathcomparator 320 configured to enable the enable pulse 352 when thevoltage pulse 312 exceeds a first threshold. In some embodiments, thefirst threshold may be relatively high to minimize detection of a falsepulse by the first path comparator 320. For example, the first paththreshold may be in the range of 5 mV to 500 mV.

In some embodiments, the second signal path 328 may comprise a secondpath comparator 348 configured to generate the digital output pulse 352when the enable pulse 324 of the first signal path 316 is enabled andthe voltage pulse 312 received from the RTIA 308 exceeds a secondthreshold, such as a threshold in the range of 10 mV to 1000 mV(referred to the RTIA output). In some embodiments, the voltage pulse312 may be passed through a series of high-pass amplifiers to yield ahigher resolution voltage pulse 344 to be used as an input of the secondpath comparator 348.

The series of high-pass amplifiers may comprise any suitable number ofamplifiers to yield a desired waveform. In some embodiments, the seriesof high-pass amplifiers may comprise a first amplifier 332 configured togenerate a first waveform 336 and a second amplifier 340 configured togenerate the higher resolution voltage pulse 344. In some embodiments,the amplifiers may have a relatively large bandwidth thereby allowingmore frequencies to pass to yield a higher resolution signal. In someembodiments, the amplifiers may have a roll-on frequency in the range of50 to 500 MHz and a roll-off frequency in the range of 100 to 5000 MHz.The relatively large bandwidth, however, may allow increased noise topass and may potentially cause a false pulse to be detected. To preventthe false pulse from being transmitted as the output pulse 352, thesecond path comparator may generate the output pulse 352 only when theenable pulse 324 is enabled. That is, the first signal path 316 may beconfigured to detect a valid pulse and to apply time domain filtering togate the second signal path 328 when the valid pulse is detected.

In some embodiments, the signal delay of the first signal path 316 maybe different from the signal delay of the second signal path 328. Theamplifiers 332 and 340 of the second signal path 328 may be selected toimprove synchronization with the first signal path 316. For example, thesecond amplifier 340 may be configured to narrow a pulse width and toincrease an amplitude of the higher resolution voltage pulse 344 sodetection of a voltage peak occurs when a corresponding enable pulse 324is enabled.

FIG. 6 illustrates an example of signals generated by the circuit ofFIG. 5. In some embodiments, the voltage pulse 312 may be output fromthe RTIA 308 and may be directed to the first signal path 316 and thesecond signal path 328. The first signal path 316 may direct the voltagestep 312 to the first path comparator 320 to enable the enable pulse 324when the first threshold is exceeded.

The second signal path 328 may direct the voltage pulse 312 to the firstamplifier 332 to yield the first waveform 336. The first waveform may bedirected to the second amplifier 340 to yield the higher resolutionvoltage pulse 344. In some embodiments, the higher resolution voltagepulse 344 may have a narrower pulse width and a larger voltage peak thanthe first waveform 336. In some embodiments, the higher resolutionvoltage pulse 344 may have an inverted peak.

FIG. 7 illustrates an example of a method 400 for generating an outputpulse using a circuit comprising an RTIA and a high-pass amplifier. Themethod may begin at step 404 where an RTIA receives a current pulse. Atstep 408, the RTIA may convert the current pulse to a voltage pulse.

The voltage pulse generated by the RTIA may be directed to a firstsignal path and a second signal path at step 412. The first signal pathmay generate an enable pulse at step 416 when the voltage step exceeds afirst threshold. In some embodiments, the first signal path may beconfigured to minimize the likelihood of the detecting a false pulse.For example, the first threshold may be relatively high to prevent thefirst signal path from enabling the enable pulse due to the detection ofnoise, rather than the signal. At step 420, the enable pulse may bedirected to the second signal path.

The second signal path may receive the voltage pulse from the RTIA andmay filter the voltage pulse at step 424. In some embodiments, thesecond signal path may filter the voltage step with a first and a secondhigh-pass amplifier to yield a higher resolution voltage pulse. Forexample, the first and second amplifiers may have a relatively widebandwidth to allow lower frequencies, which may potentially be signal ornoise, to pass. In some embodiments, passing the signal through theseries of amplifiers may sharpen the waveform by narrowing the pulsewidth and/or increasing the peak amplitude. The sharpened waveform mayallow for better detection of the voltage peak.

At step 428, the second signal path may generate a digital outputvoltage when the higher resolution voltage pulse exceeds a secondthreshold and the enable pulse is enabled. In some embodiments, thesharpened waveform output by the second amplifier of the second signalpath may allow the peak to be detected at substantially the same timethat a corresponding enable pulse is enabled. The method then ends.

Modifications, additions, or omissions may be made to the methodsdescribed without departing from the scope of the invention. The methodsmay include more, fewer, or other steps. Additionally, steps may beperformed in any suitable order.

Although this disclosure has been described in terms of certainembodiments, alterations and permutations of the embodiments will beapparent to those skilled in the art. Accordingly, the above descriptionof the embodiments does not constrain this disclosure. Other changes,substitutions, and alterations are possible without departing from thespirit and scope of this disclosure, as defined by the following claims.

1.-12. (canceled)
 13. A circuit comprising: a Resistive Trans-ImpedanceAmplifier (RTIA) configured to: receive a current pulse at an input; andconvert the current pulse to a voltage pulse; a first signal pathconfigured to: receive the voltage pulse from the RTIA; and generate anenable pulse when the voltage pulse exceeds a first threshold; and asecond signal path configured to: receive the voltage pulse from theRTIA; receive the enable pulse from the first signal path; and generatean output pulse when the voltage pulse exceeds a second threshold andthe enable pulse is enabled; and the second signal path comprising afirst and a second high-pass amplifier configured to increase detectionof the voltage pulse.
 14. The circuit of claim 13, the first signal pathfurther comprising: a first path comparator configured to enable theenable pulse when the voltage pulse exceeds the first threshold, thefirst threshold selected to minimize detection of a false pulse by thefirst path comparator.
 15. The circuit of claim 13, the second signalpath further comprising: a second path comparator configured to generatethe output pulse when the voltage pulse exceeds the second threshold andthe enable pulse is enabled.
 16. The circuit of claim 13, the secondamplifier configured to narrow a pulse width of the voltage pulse toincrease detection of a voltage peak.
 17. The circuit of claim 13, thecurrent pulse input received from a sensor of a Laser Detection andRanging (LADAR) system, the sensor configured to detect a laser pulsereflected by a target object.
 18. A method comprising: receiving acurrent pulse at an input of a Resistive Trans-Impedance (RTIA)amplifier; converting the current puke to a voltage pulse; directing thevoltage pulse to a first signal path and a second signal path; receivingthe voltage pulse at the first signal path; generating, by the firstsignal path, an enable pulse when the voltage pulse exceeds a firstthreshold; directing the enable pulse to a second signal path; receivingthe voltage pulse and the enable pulse at the second signal path; andgenerating, by the second signal path, an output pulse when the voltagepulse exceeds a second threshold and the enable pulse is enabled, thesecond signal path comprising a first and a second amplifier to increasedetection of the voltage pulse.
 19. The method of claim 18, thegenerating the enable pulse further comprising: enabling the enablepulse when the filtered voltage pulse exceeds the first threshold at afirst path comparator, the first threshold selected to minimizedetection of a false pulse by the first path comparator.
 20. The methodof claim 18, the generating the output pulse further comprising:determining, by a second path comparator, when the voltage puke exceedsthe second threshold and the enable pulse is enabled.
 21. The method ofclaim 18, the second amplifier further configured to perform the stepof: narrowing a pulse width of the voltage pulse to increase detectionof a voltage peak.
 22. The method of claim 18, the receiving the currentpulse further comprising: receiving the current pulse from a sensor of aLaser Detection and Ranging (LADAR) system, the sensor configured todetect a laser pulse reflected by a target object,